The objectives of this project are to continue and to expand research on the mapping of normal banded human chromosomes through measurements of relative positions of C-, G-, and R-bands. Major chromosomes in the human complement will be analyzed through single and multiple line scannings obtained with a scanning photometer associated to a programmable calculator. A special computer program will be developed for this project. This program will allow detecting of densitometric peaks corresponding to major bands, to give their relative band positions and to analyze them statistically. Relative G- and R-band positions will be compared with relative positions of the points of sister chromatid exchanges induced by bromodeoxyuridin in chromosomes from the same individual. As a result of this study the data obtained will be compared with the Paris (1971), New York (1974) and Edinburgh (1975) nomenclatures and chromosome landmarks will be re-defined in terms of their relative positions. This new mapping methodology would be useful for describing all kinds of band patterns as well as for detecting minor chromosome structural changes related to human chromosome variability and new pathological conditions.